Relationship of midtrimester fetal fibronectin (FFN) concentration to antibiotic efficacy for the prevention of spontaneous preterm birth in asymptomatic FFN positive women

Abstract

To evaluate whether pretreatment midtrimester quantitative cervicovaginal FFN concentration is related to antibiotic efficacy for the prevention of spontaneous preterm birth (SPTB) in asymptomatic FFN positive women. This study is a secondary analysis of a multicenter double-blind, placebo-controlled trial of antibiotic therapy for asymptomatic women with a positive cervicovaginal FFN (≥50 ng/mL) at 21-25 wks gestation. Women were randomized to receive either metronidazole 250 mg tid plus erythromycin 250 mg qid for 10 days or identical appearing placebo. The primary study outcome was SPTB <37 wks. Quantitative FFN concentrations were determined by ELISA. Of the 715 women enrolled, 699 had quantitative FFN values and outcomes available. No differences were noted between treatment groups with respect to age, race, gestational age at randomization, history of spontaneous preterm birth, or bacterial vaginosis status. Forty six percent of women had FFN values from 50-99 ng/mL, 17% from 100-149 ng/mL, 8% from 150-199 ng/mL, and 29% ≥200 ng/mL. Overall incidence of SPTB was 13.4%. The incidence of SPTB increased significantly with increasing quantitative FFN concentration: 12% 50-99 ng/mL, 13% 100-149 ng/mL, 27% 50-199 ng/mL, and 23% ≥200 ng/mL (P = .0002). No differential effect of antibiotic therapy, however, was noted on the incidence of SPTB relative to quantitative FFN concentration (Table).Tabled 1SPTB <37 Weeks By Quantitative FFN Concentration vs TreatmentFFN Concentration (ng/mL)Placebo (n = 346)Antibiotic (n = 353)P value50–999.8%8.7%.85100–1498.3%11.7%.76150–19931.0%19.2%.37≥20014.0%24.2%.07 Open table in a new tab The incidence of spontaneous preterm birth <37 wks increases significantly with increasing quantitative FFN concentration. Irrespective of pretreatment cervicovaginal FFN concentration, antibiotic use in asymptomatic FFN positive women is ineffective to prevent SPTB.